Tandem master brake cylinders are known. For correct operation of a tandem master brake cylinder, it is necessary to ensure a hydraulic connection between the pressure chamber and a pressure medium reservoir both in an initial position or neutral position in an unbraked state and also, briefly, at the beginning of the braking operation or at the beginning of the movement of the piston. For this purpose, known pistons of plunger-type tandem master brake cylinders generally have a series of replenishing connections embodied as radial bores, referred to as “suction bores”.
To improve behavior when braking is initiated, especially to ensure a reliable hydraulic connection to the pressure medium reservoir and to avoid play or a pedal idle travel, the known prior art (e.g. DE102004048670A1, DE60208806T2) which is incorporated by reference, also has further modifications. For example, the prior art includes plunger-type tandem master brake cylinders for hydraulic motor vehicle brake systems, the secondary pistons of which have “anti-cavitation” or “pilot” bores in addition to a single row of suction bores. This is a row of additional through openings offset relative to the plane of the suction bores, counter to the actuating direction, with the result that they are closed later during closure, the cumulative passage area of which openings is significantly less than the passage area of the suction bores.
In many known brake systems, the aim is to keep a pedal idle travel as short as possible in order to achieve a rapid braking force buildup after as short a time delay as possible.
Among the factors that are regarded as disadvantageous in known systems is the fact that a short pedal idle travel and a subsequent steep pressure rise in such systems can lead to severe losses of comfort, e.g. owing to a hard, unpleasant pedal feel or greater noise generation due to abrupt deceleration of a brake booster piston or diaphragm plate coupled to the tandem master brake cylinder with a control housing.
It is furthermore known that dynamic effects can lead to noise due to the deceleration of the internal parts of a pneumatic brake booster if the inflowing atmospheric volume comes to a halt ad hoc when it runs up against the hydraulic column in the chambers of the tandem master brake cylinder after the hydraulic closing travel in the tandem master brake cylinder has been traversed by the pistons. There is “application knock”.